The present invention relates to electronic oscillator circuits. In particular, the present invention relates to a method and apparatus that provides for an oscillator that includes a thermal feedback loop.
Oscillator circuits are common building blocks in analog and digital electronic systems. Some example applications of oscillator circuits include: a source of regularly spaced pulses such as for a xe2x80x9cclockxe2x80x9d in a digital electronic system, an accurate time base in a frequency counter, a local oscillator in a transceiver circuit, as well as any other appropriate use.
An example of an RC oscillator circuit (100) is shown in FIG. 1. Oscillator circuit 100 includes a comparator (110), four resistors (R10-R13), and a capacitor (C1).
The comparator (110) includes a non-inverting input (+) that is connected to a node (N10), an inverting input (xe2x88x92) that is connected to a node (N11), and an output terminal that is connected to a node (N12). Resistor R10 is connected between node N10 and node N12. Resistor R13 is connected between node N11 and node N2. The capacitor (C1) is connected between node N11 and node N13. Resistor R11 is connected between node N10 and node N14. Resistor R12 is connected between node N10 and node N15.
In operation, the RC oscillator circuit (100) produces an output signal at node N12. A power supply signal (Vcc) is connected to node N14, while a ground potential is connected to node N13. The comparator (110) produces a signal at node N12 in response to a comparison of the potentials at the non-inverting (+) and inverting (xe2x88x92) terminals. (i.e., VN12=Avxc2x7(VN10xe2x88x92VN11), where Av=open loop gain of the comparator). The signal at node N12 is a rail-to-rail signal that drives into R13 and C1. The time constant associated with R13 and C1 determines the oscillation frequency of the oscillator circuit (100). Resistors R10, R11, and R12 determine the signal level of the oscillator circuit (100). When resistors R10, R11, and R12 are of equal values, the oscillator circuit (100) will produce a voltage between ⅓ Vcc and ⅔ Vcc at the non-inverting input (+)
As described above, oscillator circuit 100 requires an exact value for R13 and C1 to change the oscillation frequency. A quartz oscillator circuit may be employed to improve frequency stability of an oscillator circuit. The use of quartz crystals and RC tuned oscillators are generally adjusted by non-integrated (xe2x80x9coff-chipxe2x80x9d) components.
The present invention is directed to a method and apparatus that produces a controlled oscillation utilizing the inherent thermal properties of silicon. A thermal oscillator includes a comparator circuit, two heat sources, and two thermal sensors. The comparator circuit controls the heat sources. Heat transfers to the thermal sensors forming a thermal feedback loop. The comparator circuit is arranged to respond to the thermal feedback to form the oscillator. A temperature control circuit is utilized to bias the temperature threshold levels for the thermal sensors. The temperature threshold level will determine an operating frequency for the thermal oscillator.
Briefly stated, a method and apparatus is directed to generating an oscillation frequency utilizing the thermal heat transfer properties of semiconductor material as a feedback loop in an oscillator. The oscillator includes a comparator that compares two input signals and enables one of two heater circuits. Each heater circuit is thermally coupled to a sensor and reference circuit. Each sensor and reference circuit pair is arranged such that the reference circuit is heated while the sensor cools. The combination of each sensor and reference circuit produces input signals for the comparator. The frequency of the oscillator is determined by the heat transfer rate between the heater circuit and the corresponding sensor, and the thermal cooling rate of the other sensor. Changing the biasing currents, and distances between the heat sources and the thermal sensors adjust the duty cycle and frequency.
In accordance with an embodiment of the present invention, an apparatus is directed to producing an oscillation frequency utilizing the thermal heat transfer characteristics of a semiconductor material. The apparatus includes a heat circuit that is arranged to selectively produce a heat signal in response to the output signal. A thermal sensor circuit is arranged to produce a sense signal in response to the heat signal. A reference circuit is arranged to produce a reference signal in response to the sense signal. A comparator circuit is arranged to produce the output signal in response to the reference signal such that the output signal oscillates between two signal levels at the oscillation frequency, wherein the oscillation frequency is determined by a time constant associated with the heat transfer characteristics of the semiconductor material.
In accordance with another embodiment of the present invention, an apparatus is directed to producing an oscillation frequency utilizing the thermal heat transfer characteristics of a semiconductor material. The thermal oscillator includes a heat circuit that is arranged to selectively produce a heat signal in response to the output signal. A reference circuit is arranged to produce a reference signal. A thermal sensor circuit is arranged to produce a sense signal in response to the heat signal and the reference signal. A comparator circuit is arranged to produce the output signal in response to the sense signal such that the output signal oscillates between two signal levels at the oscillation frequency, wherein the oscillation frequency is determined by a time constant associated with the heat transfer characteristics of the semiconductor material.
In accordance with yet another embodiment of the present invention, a method is directed to producing an oscillation signal with a corresponding oscillation frequency and duty cycle utilizing thermal heat transfer characteristics of a semiconductor material. The method includes comparing a first input signal and a second input signal with a comparator, producing the output signal in response to the comparison, activating a first heat source to produce first heat signal in response to the output signal when the output signal corresponds to a first logic level, activating a second heat source to produce a second heat signal in response to the output signal when the output signal corresponds to a second logic level that is different from the first logic level, sensing the first heat signal to produce a first sense signal with a first thermal sensor, sensing the second heat signal to produce a second sense signal with a second thermal sensor, producing the first input signal in response to the first sense signal, and producing the second input signal in response to the second sense signal such that the output signal oscillates between the first and second logic level at a rate corresponding to the oscillation frequency.
In accordance with still another embodiment of the present invention, an apparatus is directed to producing an output signal with a corresponding oscillation frequency utilizing the thermal characteristics of a semiconductor material. The apparatus includes a comparison means that is arranged to produce an output signal in response to a comparison between a first input signal and a second input signal. A first heat means is arranged to produce a first heat signal when the output signal is a first logic level. A second heat means is arranged to produce a second heat signal when the output signal is a second logic level that is different from the first logic level. A first sense means is arranged to produce the first input signal in response to the first heat signal. A second sense means is arranged to produce the second input signal in response to the first heat signal, wherein the first and second input signals form a differential input signal for the comparison means such that output signal oscillates between the first and second logic levels at an oscillation frequency that is related to the thermal characteristics of the semiconductor material.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are embodiments of the invention briefly summarized below, to the following detail description of presently preferred, and to the appended claims.